|Publication number||US7400146 B2|
|Application number||US 10/513,526|
|Publication date||Jul 15, 2008|
|Filing date||May 7, 2003|
|Priority date||May 8, 2002|
|Also published as||EP1506416A1, US20050156595, WO2003096043A1|
|Publication number||10513526, 513526, PCT/2003/1765, PCT/IB/2003/001765, PCT/IB/2003/01765, PCT/IB/3/001765, PCT/IB/3/01765, PCT/IB2003/001765, PCT/IB2003/01765, PCT/IB2003001765, PCT/IB200301765, PCT/IB3/001765, PCT/IB3/01765, PCT/IB3001765, PCT/IB301765, US 7400146 B2, US 7400146B2, US-B2-7400146, US7400146 B2, US7400146B2|
|Inventors||Cornelis Leonardus Gerardus Ham, Nicolaas Bernardus Roozen, Patrick Willem Paul Limpens|
|Original Assignee||Koninklijke Philips Electronics N.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (1), Referenced by (1), Classifications (8), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to a magnetic resonance imaging apparatus which includes a magnetic main system for generating a magnetic main field in an examination volume space which is situated within the magnetic main system, a magnetic gradient coil system which is provided between the magnetic main system and the examination volume in order to generate at least one gradient of the magnetic main field, and a vacuum space, the gradient coil system only partially adjoining the vacuum space.
A magnetic resonance imaging apparatus of the kind set forth is known from DE-C1-19940550. In this known apparatus a tubular vacuum space is situated between the enclosures of the magnetic gradient coil system and of the magnetic main system, that is at the side of the gradient coil system which is remote from the examination volume. The object is to achieve a reduction of the noise volume which is caused by the operation of the magnetic resonance imaging apparatus. Even though in practice the noise is indeed reduced to some extent, it has been found in particular that the advantageous effect for the patient present in the examination volume remains only limited.
Reference is also made to U.S. Pat. No. 6,043,653. In order to limit annoying noise caused by vibrations of the gradient coil system, the magnetic resonance imaging apparatus described therein is provided with a vacuum chamber which completely encloses the gradient coil system. One cylindrical wall portion of the vacuum chamber extends between the gradient coil system and an RF transmission coil system, while another cylindrical wall portion of the vacuum chamber is formed by the enclosure of the magnetic main system. Even though a construction of this kind indeed yields a reduction of the noise which is larger than that achieved in the magnetic resonance imaging apparatus disclosed in DE-C1-19940550, such a set-up also has drawbacks which are notably of a constructional nature. This also becomes manifest as a high cost price. Because the gradient coil system is situated completely within the vacuum space, it is necessary to use gastight passages through the wall of the vacuum chamber for the leads, such as supply cables and ducts for cooling liquid which are connected to the gradient coil system. The same holds for the feet via which the gradient coil system rests on the base. These feet, evidently engaging the gradient coil system, extend, via a gastight passage, to outside the vacuum chamber. Severe requirements in respect of gastightness are imposed on such passages; in this respect, a complicating factor is formed by the inherent vibrations whereto various parts of the magnetic resonance imaging apparatus are subject. It is also to be noted that small discharge phenomena could occur at the prevailing pressures of from approximately 1 to 10 mbar; such phenomena may notably be due to the supply cable for the gradient coil system and other connections. Discharge phenomena of this kind may have a strong adverse effect on the operation of the relevant magnetic resonance imaging apparatus. In order to avoid such phenomena, it is necessary to take additional constructional steps, for example, in the form of insulation facilities.
In order to generate an as homogeneous as possible magnetic field in the examination volume while keeping the construction as compact as possible, the apparatus which is known from U.S. Pat. No. 6,043,653 utilizes metal rods which are positioned in axially oriented ducts in the wall of the gradient coil system. The magnetic resonance imaging apparatus can thus be tuned to the specific environment in which it is used, that is, in dependence on the characteristics of the environment in which the magnetic resonance imaging apparatus operates, for example, steel reinforcements in a concrete floor on which the magnetic resonance imaging apparatus is erected and possibly also for compensation of manufacturing tolerances. In practice this is realized by positioning metal rods of suitable thickness in a rail system which is made of a non-magnetic material such as stainless steel or aluminum. Such rails are also referred to as “shim rails” and the metal rods as “shim irons”. Shim irons of optimum thickness can thus be positioned in the correct positions in the ducts. The process for the adjustment of the magnetic resonance imaging apparatus is considerably hampered by the presence of the vacuum chamber which must be opened for this purpose.
Because the vacuum chamber in the cited U.S. Pat. No. 6,043,653 completely encloses the gradient coil system, the vacuum chamber extends, viewed in the axial direction, beyond the gradient coil system, so that a comparatively long tunnel is formed for the patient. Consequently, a patient positioned in the examination volume will more readily experience claustrophobic sensations. Moreover, the room for movement of the medical staff is also limited, so that it is more difficult or even impossible to carry out medical tasks on a patient in the examination volume.
It is an object of the invention to provide a solution to or at least an improvement for the above drawbacks, whether or not in preferred embodiments of the invention, where notably a substantial noise reduction is achieved for a patient present in the examination volume.
In order to achieve this object, a magnetic resonance imaging apparatus in accordance with the invention is characterized in that the gradient coil system adjoins the vacuum space by way of a side which faces the examination volume. Radiation of sound waves directly from the gradient coil system to the patient is thus prevented, resulting in a substantial reduction of the noise volume experienced by the patient.
A constructionally simple and hence advantageous solution is offered by a special embodiment of a magnetic resonance imaging apparatus in accordance with the invention in which the vacuum space is bounded by a mainly cylindrical wall which is situated between the examination volume and the gradient coil system and forms an integral part of an RF transmission coil system for generating an RF signal in the examination volume. An RF transmission coil system of this kind and its function are known to a person skilled in the art and need not be elucidated herein.
A further embodiment of a magnetic resonance imaging apparatus in accordance with the invention is characterized in that the RF transmission coil system includes an RF transmission coil which is attached to said wall. It is thus achieved that the individual parts can be optimally tuned to their specific function.
Considering the fact that the axial length of the RF transmission coil system usually is shorter than that of the gradient coil system, with a view to further increasing the noise reducing effect it is very advantageous when the wall has an axial length which is greater than an axial length of the RF transmission coil system. It is thus achieved that the part of the gradient coil system which is situated outside the RF transmission coil system is also shielded at least partly.
A very advantageous preferred embodiment is obtained when an RF transmission coil shield which forms part of the RF transmission coil system is situated within the vacuum space. Such an RF transmission coil shield, serving to prevent RF radiation from reaching the gradient coil system, is more effective as the distance between the RF transmission coil shield and the RF transmission coil, also forming part of the RF transmission coil system, is larger. Therefore, the vacuum space constitutes a very attractive position for the RF transmission coil shield. It has been found that the effectiveness of the RF transmission coil shield is not influenced by the fact that the RF transmission coil shield is situated in a space in which a reduced pressure prevails.
A constructionally simple solution is obtained in a further embodiment of a magnetic resonance imaging apparatus in which the vacuum space is sealed by means of sealing means which adjoin the gradient coil system and said wall.
A special embodiment of a magnetic resonance imaging apparatus in accordance with the invention, in which an advantageous compromise is reached between the noise reduction and the constructional complexity of the magnetic resonance imaging apparatus, is characterized in that the gradient coil system adjoins the vacuum space exclusively by way of its side which faces the examination volume.
In order to increase the noise reducing effect further, a further embodiment of the magnetic resonance imaging apparatus in accordance with the invention is provided with a further vacuum space which is situated between the gradient coil system and the main coil system. It is very advantageous if a connection exists between the vacuum space and the further vacuum space, so that these spaces together constitute a common vacuum space. The advantageous effect is due to the fact that means for the common vacuum space have to be provided in singular form only in order to realize the reduced pressure in the common vacuum space. In order to avoid external ducts, it is also advantageous when the connection extends through the gradient coil system.
A special embodiment of a magnetic resonance imaging apparatus in accordance with the invention is characterized in that the gradient coil system comprises two end sides, at least one end side adjoining an atmospheric space. Said at least one end side is excellently suitable for engagement or connection of facilities to the gradient coil system, so that a vacuumtight passage through a wall enclosing the vacuum space can be dispensed with. Said end side does not adjoin the vacuum space, so that at the area of this end side mechanical vibrations of the gradient coil system are converted into sound vibrations. Said end side, however, has a comparatively small surface area, so that said sound vibrations are of limited strength only and hence are not experienced as being annoying.
In a special embodiment of a magnetic resonance imaging apparatus in accordance with the invention an electrical power supply cable for the gradient coil system adjoins said at least one end side of the gradient coil system, so that no vacuumtight passage is required for said electrical power supply cable.
In a further embodiment of a magnetic resonance imaging apparatus in accordance with the invention, the gradient coil system is supported on a base for the magnetic resonance imaging apparatus via the at least one end side of the gradient coil system, so that no vacuumtight passage is required for the structural parts required for such support. Preferably, for the support a constructional connection is provided between the gradient coil system and the magnetic main system, so that supporting is also realized via the magnetic main system. Furthermore, a connection of this kind can provide constructionally simple correct mutual positioning of the magnetic main system and the gradient coil system. In addition, the support can also perform the function of isolating vibrations by utilizing a comparatively flexible connection which is attached to a comparatively rigid area of the magnetic main system. It is advantageous if the magnetic main system comprises an enclosure in the form of a tube whose wall is hollow so as to accommodate a main coil of the main system, said tube having a cylindrical inner wall, a cylindrical outer wall and sealing walls which extend between the ends of the inner wall and the outer wall; the constructional connection therein acts on a sealing wall in the immediate vicinity of the inner wall and/or the outer wall. This location for engagement by the connection offers a high constructional stiffness.
The invention will be described in detail hereinafter with reference to a preferred embodiment of a magnetic resonance imaging apparatus in accordance with the invention. For this description reference is made to the following diagrammatic Figures:
The magnetic resonance imaging apparatus 1 as shown in
The magnetic resonance imaging apparatus 1 is provided with an examination volume 7 which is situated around its center line 6 and serves to accommodate a patient. To this end, the patient is slid into the volume 7 while resting on a support. The facilities required for this purpose are not shown in the Figures. Inside the gradient coil system 3 there is situated, that is, at the center when viewed axially, an RF transmission coil system 8 which is coaxial with the gradient coil system 3 and provided with an RF transmission coil (not shown) and an RF transmission coil shield (not shown), the length of which amounts to approximately half of that of the gradient coil system 3.
In the conical side faces 9 to both sides of the gradient coil system 3 there are provided ducts 10 which extend in the axial direction and can receive metal rods (shim plates) 11. The magnetic characteristics of the magnetic resonance imaging apparatus 1 can be tuned to the environment in which the magnetic resonance imaging apparatus 1 operates, and also to the characteristics of the apparatus 1 itself, by suitably choosing the position and the length and the thickness of said plates 11. The magnetic resonance imaging apparatus 1 bears on a base by way of four legs 12 which engage the enclosure 4.
Images of the inside of a patient can be formed by means of the superconducting windings of the magnetic main system 2, the gradient coils of the gradient coil system 3 and the RF transmission coil of the RF transmission coil system 8, that is, under the control of a control system (not shown) which forms part of the magnetic resonance imaging apparatus 1. The electromagnetic forces then occurring give rise to vibrations of the gradient coils of the gradient coil system 3, which vibrations are capable of producing a noise with a high volume which is very annoying to a patient present within the examination volume 7. In order to limit the annoying properties of such a noise, a mainly closed cylindrical space 13 is formed between a tubular sealing member 14 and the gradient coil system 3 on the inside of the gradient coil system 3, as shown in
At the ends of the sealing member 14 flexible rubber sealing rings 15 are provided between the sealing member 14 and the enclosure of the gradient coil system 3. Alternatively, the sealing rings may also be made of, for example, plastic. It is important that the material enables vacuumtight sealing. Moreover, the connection of the sealing rings 15 should not be too stiff. Excessive transfer of mechanical vibrations from the gradient coil system 3 to the sealing member 14 is thus prevented, since otherwise the noise reducing effect pursued by the invention would be canceled again.
The volume 13 is connected to a vacuum pump 18, via a bore 16 in the sealing member 14 and a connecting tube 17, said vacuum pump being capable of reducing the pressure in the volume 13. Consequently, vibrations of the gradient coils of the gradient coil system 3 will produce sound waves to a lesser extent, notably in the examination volume 7.
A further improvement in this respect is achieved in that on the outside of this gradient coil 3 there is also situated a mainly closed cylindrical space 19 in that rubber sealing rings 20 are provided between the axial ends of the enclosures of the gradient coil system 3 and the main coil system 2. Alternatively, such sealing rings may also have a constructional supporting function for the supporting and/or mounting the gradient coil system 3. The space 19 communicates with the space 13 via a radially oriented passage 21 through the gradient coil system 3. The vacuum pump 18 thus also reduces the pressure in the space 19, so that a larger part of the gradient coil system 3 is enclosed by a space with a reduced pressure. Alternatively, it may even be more advantageous to replace the bore 16 by a bore which extends from the end side 22 of the gradient coil system 3 to the space 13 and the space 19, so that more room is now available for the patient in the examination volume 7.
As is clearly shown in
The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US20130314089 *||Jul 11, 2013||Nov 28, 2013||Toshiba Medical Systems Corporation||Magnetic resonance imaging apparatus|
|U.S. Classification||324/318, 324/307|
|International Classification||G01R33/28, A61B5/055, G01V3/00, G01R33/385|
|Nov 4, 2004||AS||Assignment|
Owner name: KONINKLIJKE PHILIPS ELECTRONICS N.V., NETHERLANDS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HAM, CORNELIS LEONARDUS GERARDUS;ROOZEN, NICOLAAS BERNARDUS;LIMPENS, PATRICK WILLEM PAUL;REEL/FRAME:016443/0005
Effective date: 20031201
|Feb 27, 2012||REMI||Maintenance fee reminder mailed|
|Jul 15, 2012||LAPS||Lapse for failure to pay maintenance fees|
|Sep 4, 2012||FP||Expired due to failure to pay maintenance fee|
Effective date: 20120715